It is becoming a common requirement for portable communications devices, such as mobile phones, to be able to operate in two separate regions of the radio frequency spectrum. For example, it is becoming a common requirement for mobile phones that they should be able to operate at 900 MHz and at 1800 MHz. Such products are known as dual-band products. In the design of such dual-band products, one option is to duplicate the receiver circuitry. U.S. Pat. No. 4,584,716 shows a radio receiver, for receiving signals at two different frequencies, in which the receiver circuitry, including radio frequency amplifier, mixer for downconversion to an intermediate frequency, intermediate frequency filter, intermediate frequency amplifier, and analog-digital converter, is duplicated.
Clearly, it would be advantageous to avoid such duplication, to reduce the size and power consumption of the device. However, any changes for this reason must also take account of the fact that radio frequency components are typically optimised for use at one particular frequency band.